Asbestos gaskets, metallic gaskets, and gaskets formed by laminating asbestos and metallic materials have heretofore been known as engine cylinder head gaskets and gas sealing gaskets for turbochargers. Particularly, gaskets for engine cylinder heads are required to improve the sealing performance upon demand for reduction in the size and weight of engines. To satisfy the requirement for the performance, metal gaskets have recently been used.
To improve the sealing performance of the metal gaskets, various structures have heretofore been proposed. As one example of these metal gasket structures, Japanese Utility Model Application Laid-Open Publication (KOKAI) No. 57-59952 (JP, U, 57-59952) discloses a gasket wherein a gasket base is elastically deformed to form a plurality of corrugate projections at the outer periphery of a combustion chamber, that is, a gasket provided with beads. The gasket is pressed from both sides of the beads, thereby deforming the beads, and thus improving the sealing performance by making use of the restitution of the deformed beads.
This gasket has excellent sealing performance. However, although the sealing performance is improved, when the gasket is clamped from both sides thereof, the beads are deformed into a flat surface and, at this time, stress concentrations occur at the angular portions of the beads. During use of the gasket for a long period of time, the metal constituting the portions having stress concentrations is fatigued by vibrations caused by explosion in the engine and this fatigue of the metal may cause breakage or weaken the elastic restoring force even if the gasket is not broken. In addition, the gasket needs a bending process to form corrugate beads in manufacture. The bending process causes work hardening and strain in the gasket base, thus the base being weakened in terms of the metallographic structure. It is also necessary to prepare a press die for the bending process.
Japanese Utility Model Application Laid-Open Publication (KOKAI) No. 60-18247 (JP, U, 60-18247) discloses a metal gasket made from a steel plate wherein beads which are in the form of recesses and projections, that is, annular grooves, are formed on both surfaces of the metal gasket so as to surround a water hole and the annular grooves are coated with a sealing material consisting essentially of a silicone resin.
This gasket needs a bending process to form beads in the same way as in the case of the above-described gasket. This gasket is a water hole gasket for waterproof sealing and has no idea for sealing engine cylinder bores that are exposed to high-temperature flame heat. In the foregoing prior arts, when the cylinders of an engine and the cylinder head, for example, are clamped by means of bolts with a gasket being interposed therebetween, the gasket is compressed unevenly, resulting in the sealing effectiveness varying depending upon the position on the gasket.
In general, gaskets have a tendency to be clamped in such a manner that the bolted portions and vicinities are strongly clamped, and the remoter therefrom, the lower the level of clamping force. This is due to the deformation of the cylinders and the cylinder head. Since cylinders and cylinder heads of engines which are reduced in size and weight as in recent years have a tendency to be reduced in the wall thickness, uneven deformation is unavoidable.